I. Field & Utility Summary
The present invention relates to a new and distinct variety of apple tree. The apple tree is particularly useful in that it can be propagated clonally and used as a rootstock or root system for apple trees as well as for interstems of apple trees. The new variety is a dwarfing rootstock that is resistant to fire blight and crown rot. It is precocious and highly productive, and can be used as a rootstock and for interstems of apple trees.
II. Cultivation Summary
‘G.222’ originated from a planned cross in 1975 in Geneva, N.Y.
III. Comparisons
The seed parent Malus domestica ‘Malling 27’ is a super-dwarfing rootstock, i.e., trees grown on this rootstock are 15 to 20 percent the size of a standard self-rooted seedling tree. ‘Malling 27’ is known to induce good precocity to the scion (i.e., the ability to induce early reproductive development in the scion) and has high yield efficiency. ‘Malling 27’ may induce small fruit size in some scion cultivars. ‘Malling 27’ plants produce no spines, are poorly anchored, and are very sensitive to drought and winter cold. They are also susceptible to the woolly apple aphid (Eriosoma lanigerum) and to fire blight (Erwinia amylovora).
The pollen parent Malus robusta ‘Robusta 5’ is a non-dwarfing rootstock, i.e. trees on this rootstock are the same size as a standard self-rooted tree. ‘Robusta 5’ does not induce precocity to the scion and is not highly yield efficient. Juvenile plants of ‘Robusta 5’ produce many spines. ‘Robusta 5’ breaks buds very early in the spring and is winter hardy. It is resistant to powdery mildew (Podosphaera leucotricha) and fire blight, and is immune to the woolly apple aphid. Further, ‘Robusta 5’ has shown tolerance to the specific replant disease complex.
The ‘G.222’ apple rootstock of the present invention has a combination of qualities that distinguishes it from its parental plants (i.e., ‘Malling 27’ and ‘Robusta 5’). For example, although ‘G.222’ has dwarfing properties derived from ‘Malling 27’, it is different from its dwarfing parent (i.e., ‘Malling 27’) because it produces a tree that is 45 to 55 percent of the size of a standard self-rooted seedling tree. Thus ‘G.222’ belongs to a different dwarfing vigor class than its ‘Malling 27’ parent. In particular, ‘G.222’ has dwarfing characteristics that are similar to the industry standard of Malus domestica ‘Malling 26’. ‘G.222’ shares similarities with ‘Malling 27’ in that they both induce precocity to the scion and are highly yield efficient.
With regard to its ‘Robusta 5’ parent, ‘G.222’ is distinguishable in that it is a dwarfing rootstock and is highly yield efficient, while ‘Robusta 5’ is not. However, like ‘Robusta 5’, ‘G.222’ is resistant to fire blight and the woolly apple aphid (Eriosoma lanigerum). In addition, ‘G.222’ has been shown to have some tolerance to the replant disease complex.
As discussed above, ‘G.222’ is most similar to ‘Malling 26’ in terms of dwarfing class. However, ‘G.222’ is more precocious and yield efficient than ‘Malling 26’. ‘G.222’ is resistant to fire blight whereas ‘Malling 26’ and other rootstocks in its market class are not.
IV. Breeding History
In the spring of 1975, pollen from a Malus robusta ‘Robusta 5’ apple tree was applied to emasculated flowers of a Malus domestica ‘Malling 27’ apple tree in Geneva, N.Y. In the fall of 1975, approximately 500 seeds resulting from this pollination were extracted from mature fruit derived from this cross. In the winter of 1975-76, the seeds were stratified and planted in large flats under conditions effective to germinate seeds and obtain seedlings. When germinated seedlings were about 2.5 cm tall they were inoculated with a mixture of isolates of the oomycete Phytophthora cactorum (the causal agent of crown and root rots). The flats were flooded to mid-hypocotyl level and kept at 23° C. for one week. Surviving seedlings were transplanted into individual pots.
In the summer of 1976, each of the transplanted seedlings was inoculated with approximately 106 colony forming units of the Ea 273 strain of the fire blight bacterium Erwinia amylovora by inserting a 26-gauge hypodermic syringe needle into the shoot tip. The seedling designated as #222 was one of the 45 survivors of this battery of inoculations from the same cross. All the 45 surviving plants were transplanted to the Loomis field (Geneva, N.Y.) in the fall of 1976 and allowed to grow side shoots for propagation/evaluation. In 1979, ‘G.222’ was evaluated for rooting ability, lack of spine production, and low root brittleness in a layering bed (stool bed). In 1982, 4 finished trees with ‘G.222’ rootstock were planted in a first test orchard on the Loomis farm (Geneva, N.Y.) with Malus domestica cv. ‘Northern Spy’ grafted onto this rootstock as the scion cultivar. In addition in 1983 and 1984, one and four additional finished trees with Malus domestica cv. ‘Northern Spy’ as the scion were planted in evaluation orchards. This rootstock performed well (top 20% of many rootstocks tested) in these first test trials and during 1990-1993 more material was propagated by stool bed and nursery to be entered into new trials at the Hansen Farm (Geneva, N.Y.) with Malus domestica cv. Empire and Liberty as the scion cultivars. The ‘G.222’ rootstock performed well with all the scion cultivars that were tested, having matched or exceeded the yield efficiency, productivity and precocity of commercial controls. In August of 2002, several rootstock liners of ‘G.222’ were budded with 15 different scion cultivars to test graft union compatibility—the test results showed that ‘G.222’ was compatible with all the cultivars tested. Visual observations made on stool beds in the Loomis Farm and harvested liners in years 2002 through 2011 showed the absence of natural wooly apple aphid infestations, while present in neighboring susceptible plants, indicating that ‘G.222’ is resistant to infestations of the wooly apple aphid.
V. Asexual Reproduction
Asexual reproduction of the ‘G.222’ apple rootstock has been achieved using the traditional method of clonally propagating apple rootstocks. In particular, the original seedling of the ‘G.222’ apple rootstock was planted in the Loomis field (Geneva, N.Y.) and allowed to develop into a “mother plant.” The ‘G.222’ mother plant was then used to obtain rooted liners using conventional layering procedures. The resulting liners were then planted in a row to generate a layering stool bed (also referred to as the “mother stool bed”). The living tissues (i.e. leaves, stems, roots, buds, and spines) of the mother stool bed were observed to be identical to secondary and tertiary stool bed plants. In addition to conventional layering, the ‘G.222’ apple rootstock variety has been asexually reproduced by root cuttings, by budding and grafting onto seedling and clonal rootstocks, and by tissue culture. Asexual reproduction by layering, root cuttings, budding, grafting and tissue culture in Geneva, N.Y. has shown that the claimed plant reproduces true to type through successive generations of asexual reproduction.
VI. Stability
Observations of trees from these propagations indicate that all trees have proven true to type and identical in all appearances to the original tree.